U.S. Severe Weather Forecast (Coup d'œil sur la convection)

Day Three

acus01 kwns 230719 
Storm Prediction Center ac 230718 

Day 1 convective outlook corr 1 
National Weather Service Storm Prediction Center Norman OK 
0118 am CST sun Nov 23 2014 

Valid 231200z - 241200z 

..there is an enh risk of severe thunderstorms across the western Florida 
Panhandle inland to extreme southeast Alabama and southwest Georgia... 

..there is a slight risk of severe thunderstorms from the northern Gulf Coast 
across parts of the southeast... 

..there is a marginal risk of severe thunderstorms surrounding the slight risk area 
from la to NC and extreme southeast Virginia and northern Florida... 

Corrected for spelling error 

Severe thunderstorms with the chance for damaging winds and a couple 
of tornadoes will spread east along the immediate Gulf Coast from 
Louisiana early today to parts of the south and southeast later 
today and into this evening. A couple of strong storms and possibly 
isolated damaging winds may develop along the southeast Atlantic 
coast tonight through early Monday morning. 

A vigorous midlevel shortwave trough will accelerate northeast and 
away from the Gulf Coast...across the MS Delta Region...and to the 
Tennessee Valley and central Appalachians through this evening. This wave 
will be ejected northeast in response larger-scale trough 
amplification across the central United States. As the leading wave 
and associated intense 500mb winds of 70-75kt spread from southeast 
la to the southern Appalachians through the day...a broader region 
of strong height falls across the central Continental U.S. Will contribute to 
surface cyclogenesis over the Midwest and result in a deepening 
synoptic low pressure system tracking toward the Great Lakes through 
Monday morning. 

..Gulf Coast to southeast... 
Latest observational trends support storm-scale guidance scenarios 
in the evolution of a linear convective system across the northern 
Gulf and parts of southeast la at the start of the period. Same 
guidance has remained generally consistent in depicting poor airmass 
quality amidst the convection over land areas...as well as with 
eastward extent ahead of a potentially better organized comma-head 
and arc of deep convection associated with the compact ejecting 
shortwave trough. It seems reasonable to expect that...in addition 
to outrunning true tropical maritime airmass return to the immediate 
Gulf Coast of la...the leading convective line may lose intensity 
during the morning as it outruns stronger forcing for ascent 
associated with the shortwave. 

The decay or decrease in intensity of the leading convective band 
may permit greater airmass destabilization into the afternoon from 
near and east of Mobile Bay to the western Florida Panhandle. Most recent 
guidance is consistent with earlier trends in showing a narrow axis 
of surface-based instability /SBCAPE 1000-1500 j per kg/ may evolve 
from the western Florida Panhandle inland to perhaps southwest Georgia 
coincident with diurnal heating cycle and strong low level mass and 
moisture fluxes in response to approach and passage of 70-75kt 
midlevel jet streak. At the same time...large-scale support for 
forced ascent and veering low level winds are forecast to occur as 
the middle/upper wave continues to Delaware-amplify in response to stronger 
upstream amplification. 

Despite some of these limiting factors...as stronger/remaining upper 
forcing and wind fields move across the instability axis through 
late afternoon...any convection in this regime will be fast-moving 
and pose a threat for wind damage...and perhaps a couple of 

Given the above scenario and consistency in the signal for at least 
modest surface-based destabilization in a narrow corridor coincident 
with intense low through midlevel wind fields from the western Florida 
Panhandle inland to parts of southern al/GA...it seems prudent to 
initiate a small 10 percent tornado probability over these areas 
along with an accompanying enhanced slight risk. 

Elsewhere across the slight-risk area...severe thunderstorms will be more 
isolated. Stronger deep ascent will exist from the lower MS valley 
to the lower Ohio Valley in closer proximity to the deepening cyclone 
and in the exit region of the aforementioned midlevel jet...limited 
buoyancy will lead to a lower severe weather probability with 
northward extent across the warm sector -- especially as more 
widespread convection closer to the Gulf Coast interrupts poleward 
fluxes of higher Theta-E air. 

Farther north and east along the Atlantic coast...stronger latent 
heat fluxes atop the Gulf Stream may support more robust 
boundary-layer moistening over the eastern Carolinas through early 
Monday morning. Given presence of intense low level jet and 
potentially large helicity...low probability tornado potential may 
develop over these areas during the overnight hours. 

.Carbin/leitman.. 11/23/2014 

Mesoscale Discussion

acus11 kwns 230734 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 230733 

Mesoscale discussion 1939 
National Weather Service Storm Prediction Center Norman OK 
0133 am CST sun Nov 23 2014 

Areas affected...southeastern la 

Concerning...severe potential...watch possible 

Valid 230733z - 231000z 

Probability of watch issuance...60 percent 

Summary...a watch will probably need to be considered for portions 
of southeastern la within the next 2-3 hours. Wind damage will be the primary 
threat but a qlcs mesovortex tornado risk may also accompany the 
squall line. 

Discussion...radar mosaic and surface observations over the northwestern 
Gulf during the past few hours have shown an intense qlcs tracking 
east-northeastward with the east breaks oil platform and khqi observing severe 
gusts /75 and 51 knots respectively/. The marine warm front is roughly 
30 Michigan from the la coast and will likely penetrate the coast and 
Terrebonne Parish within the next few hours as the mesolow over the 
northwestern Gulf develops northeastward into southwestern la. A more moist/unstable airmass 
S of the warm front will support a surface-based severe threat. 
Linear extrapolation shows the bowing segment within the qlcs 
approaching the coast of St. Mary and Terrebonne Parish prior to 
10z. The threat for damaging winds in the form of strong to severe wind 
gusts will probably increase across southeastern la as the warm front 
advances northward and as the qlcs approaches. Given the moist and 
strongly sheared low-level wind profile...a qlcs tornado is also 
possible with any longer-lived and stronger mesovortex. 

.Smith/Mead.. 11/23/2014 

..please see www.Spc.NOAA.Gov for graphic product... 


Latitude...Lon 29599213 29889088 30208975 29708888 29078906 29009052 
29309190 29599213